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Date: | Wed, 3 Jun 2009 16:26:13 -0500 |
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Hi Steve and TechNet - I have had a several folks ask me to provide a
further explanation the " "flux only" will have lower solder joint life
than a BGA reflowed with solderpaste". If you look at many of the solder
joint life prediction models, you will find that the solder joint height
has a significant impact on overall solder joint integrity. Take a look
at IPC-D-279, Appendix A 3.1, you will find the Engelmaier-Wild model and
the solder joint height influence is fairly easy to see. If an operator
reflows a BGA using solder paste, you will get more solder volume and
therefore a slightly increased solder joint height. With that being said,
the BGA solder joint life will be better but maybe not necessarily
required for a product use environment. As many of the TechNet responses
have shown, it is common practice to use "flux only" reflow and meet the
requirements of many IPC Class 2/IPC Class 3 use environments with no
issues. Rockwell Collins has used "flux only' practices for many years and
is just now transitioning to the new dip-able solderpastes for both
increased solder joint reliability and ease of rework procedure. Rockwell
Collins will be publishing a paper on the reliability of BGAs reworked
with a dip-able solder paste process in the near future. The dip-able
solder paste is not a new thing - many folks in the wafer bumping
technology have been using it for years.
Werner gives a much better explanation of the impact of solder joint
height than my simple attempt.
Hope this better explains my comments.
Dave
"Steve Kelly" <[log in to unmask]>
06/03/2009 03:33 PM
To
<[log in to unmask]>
cc
"'TechNet E-Mail Forum'" <[log in to unmask]>
Subject
RE: [TN] BGA-113 package
Thanks everyone for the excellent feedback. Interesting information.
Regards Steve Kelly
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: June-03-09 2:50 PM
To: Steve Kelly
Subject: Re: [TN] BGA-113 package
Hi Steve! Yes, you can reflow a BGA with "flux only" and not use
solderpaste. Just remember that solder joint integrity is a function of
the solder joint height. A BGA reflowed with "flux only" will have lower
solder joint life than a BGA reflowed with solderpaste. And lower life
doesn't not necessarily mean bad - just lower. The resulting BGA solder
joints may be perfectly acceptable for the product use environment. Good
Luck.
Dave Hillman
Rockwell Collins
[log in to unmask]
Steve Kelly <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
06/03/2009 11:10 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Steve Kelly <[log in to unmask]>
To
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cc
Subject
[TN] BGA-113 package
Hi All,
We have a rigid flex that has a BGA-113 (microstar BGA) package to be
mounted to it. The routing in this area on the top layer leaves me with
.0005 of soldermask clearance from the edge of the BGA pad and .003
distance
from the edge of the soldermask to the nearest track- in other words I
have
.0035 of clearance from pad edge to next track assuming a perfect etch and
perfect soldermask registration.
Having rooted around Texas Instruments web site I believe that it may be
possible to reflow this BGA without adding solder paste to the pad - just
letting the ball collapse do the attachment. If my scenario is correct I
could open up the soldermask and not have too many concerns about bridging
between the BGA pads and the tracks. Any thoughts or comments would be
appreciated.
Thanks Steve Kelly
Steve Kelly (PLEASE NOTE NEW E-MAIL ADDRESS)
(416) 750-8433 (work)
(416) 750-0016 (fax)
(416) 577-8433 (cell)
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